1. Field of the Invention
This invention relates to a card type fuse in which fuse circuits are arranged on an insulation substratum and in which a cover layer covers the fuse circuits, and a method of producing the same.
2. Statement of the Prior Art
A card type fuse is suitable for use in various devices having a low electrical power of less than 1A. For example, such a fuse is suitable for fuse-matching in a wire harness composed of wires having a small diameter, and which connects, for example, a series of electronic elements in a car. In such fields, utilization of card type fuses has been increasing.
For instance, in a harness for a motor car, a card type fuse is employable with reduced diameter wires and has an advantage in that it has a small capacity. Electronic elements in cars are required to connect various kinds of devices and include a number of small capacity fuses. As such, card type fuses are advantageous since they can arrange many small capacity fuses.
Ease of connection to a wiring harness has promoted the use of card type fuse-equipped connectors or the like. Such a connector is located not only in special fuse boxes but also in various kinds of devices. The connector is suitable for use with a multiple connections having a small size, thus enabling a car to be provided with numerous electronic devices.
In addition, heretofore, a low melting point metal (lead, zinc, lead-tin alloy) or a high melting point metal (silver, copper) has been used as a fuse element. However, use of a low melting point metal makes it difficult to produce a fuse having a small diameter. On the other hand, use of a high melting point metal is inappropriate in that a melting point higher than that required is provided. Such a high melting point metal can not release a circuit upon over-heating and thus makes it difficult to produce a low power circuit. In view of the above, the card type fuse is the most suitable for use in a small sized fuse circuit carrying a low current.
In Japanese Patent Publication No. 59-42479 (1984), a card type fuse is disclosed which is produced by the steps of: forming a fuse circuit on a substratum (e.g., copper-glass epoxy substratum) for a circuit sold in a market through a stainless mask in an exposuring manner; vaporizing the low melting point metal such as tin and the like on the fuse circuit; and coating the fuse circuit with a heat resisting film such as polyester (PET), polyimide (PI) or the like by using an adhesive.
However, manufacture of the above card type fuse is both time and cost inefficient and makes it difficult to precisely design an exothermic fusing portion.